This invention relates generally to migration imaging systems and more specifically, to a process of splitting an imaged migration imaging member at an interface between a first layer of softenable material containing unmigrated migration material, i.e., background material, overlying a second layer of softenable material containing migration material in image configuration. At least one of the softenable layers contains a surface skin at the interface between the softenable layers. When the imaged member is split at this interface, where the surface skin is located, an unexpected improvement in image resolution and diffuse contrast density is obtained as compared with images produced by splitting similar two-layer structures which do not contain surface skins.
A migration imaging system capable of producing high quality images of high density, continuous tone and high resolution has been developed. Such imaging systems are disclosed in copending U.S. patent application Ser. No. 837,780 and Ser. No. 837,591, both filed June 30, 1969, both of which the entire contents of which are hereby incorporated herein by reference. In a typical embodiment of these migration imaging systems, an imaging member comprising a substrate, a layer of softenable material containing electrically photosensitive migration material is latently imaged, e.g., by electrically charging the member and exposing the charged member to a pattern of activating electromagnetic radiation, such as light. When the photosensitive migration material is originally in the form of a fracturable layer located at the upper surface of the softenable material, particles of the migration material in the exposed areas of the migration member migrate toward the substrate when the member is developed by decreasing the resistance of the softenable layer sufficient to allow migration of the migration material in depth in the softenable material. When the photosensitive material is originally dispersed throughout the layer of softenable material, particles of the migration material in the unexposed areas of the migration member migrate toward the substrate when the member is developed by decreasing the resistance of the softenable layer sufficient to allow migration of the migration material in depth in the softenable material.
Various modes for developing, i.e., softening the softenable material sufficient to allow migration of the migration material in depth in the softenable material, are known. These various development modes include, e.g., softening by liquid solvents, solvent vapors, heat and combinations thereof, as well as other methods of softening the softenable material to allow migration of the migration material in depth in the softenable material, as disclosed in both Ser. No. 837,780 and Ser. No. 837,591.
The imaging systems disclosed in copending application Ser. No. 460,377, filed June 1, 1965, now U.S. Pat. No. 3,520,681, the entire contents of which are hereby incorporated herein by reference, generally comprises the combination of process steps which include forming a latent image on a migration imaging member and developing with solvent liquid or vapor or heat or combinations thereof, to render the latent image visible. In certain methods of forming the latent image, non-photosensitive or photosensitively inert, fracturable layers and particulate material may be used to form images, as described in copending application Ser. No. 583,675, filed Aug. 30, 1965, now U.S. Pat. No. 3,466,963, the entire contents of which are hereby incorporated herein by reference, wherein a latent image is formed by a wide variety of methods including charging in imagewise configuration through the use of a mask or stencil; first forming such a charge pattern on a separate photoconductive insulating layer according to conventional xerographic reproduction techniques and then transferring this charge pattern to the imaging member by bringing the two layers into very close proximity and utilizing breakdown techniques as described, for example, in Carlson, U.S. Pat. No. 2,982,647 and Walkup, U.S. Pat. Nos. 2,825,814 and 2,937,943. In addition, charge patterns conforming to selective, shaped electrodes or combinations of electrodes may be formed by the "TESI" discharge technique as more fully disclosed in Schwertz, U.S. Pat. Nos. 3,023,731 and 2,919,967 or by the techniques described in Walkup, U.S. Pat. Nos. 3,001,848 and 3,001,849 as well as by electron beam recording techniques, for example, as disclosed in Glenn, U.S. Pat. No. 3,113,179.
U.S. Pat. No. 3,741,757 discloses providing an imaged member comprising a layer of softenable material and migration material selectively distributed in depth in the softenable material in first image configuration and comprising in addition to said first image pattern of migration material, a background of substantial amounts of migration material in the softenable material but spaced apart in depth from the first image pattern and then removing the background. A specifically preferred embodiment is removing the background of migration material by splitting the softenable layer on an average in a plane substantially between the image pattern configuration of migration material and the background of migration material. Also disclosed in U.S. Pat. No. 3,741,757 is a preferred strip-splitting technique which also substantially simultaneously accompanies migration development of a latent image, i.e., applying a migration force to the migration layer of a migration imaging member sufficiently to cause migration of the migration material in image configuration and then developing the member by softening the softenable material with, for example, softening liquid for the softenable layer whereby the migration material migrates in image configuration. Then the stripping member is placed against a free surface of the softenable layer and then stripped apart to create a complementary positive and negative split image. While U.S. Pat. No. 3,741,757 discloses mainly layer configuration migration imaging members as described in U.S. patent application Ser. No. 725,676, now abandoned, U.S. Pat. No. 3,741,757 also discloses binder configuration migration imaging members as described in copending application Ser. No. 634,757, filed Apr. 28, 1967, now abandoned.
It has recently been discovered that an image may be produced by splitting which has unexpected improved properties, e.g. resolution and diffuse contrast density, when a new migration imaging member, comprising a first layer of softenable material containing migration material overlying a second layer of softenable material which is substantially devoid of migration material and at least one of the softenable layers contains a surface skin at the interface between the first and second layers of softenable material, is developed by migration imaging to form a migration imaged member comprising a first layer of softenable material containing background material, i.e., unmigrated migration material, overlying a second layer of softenable material containing imagewise migrated migration material, i.e., the migrated image, and at least one of the softenable layers containing a surface skin at the interface between the first and second layers of softenable material. The imaged member is split at the interface, where the surface skin is located, resulting in the background being removed producing an image which unexpectedly has superior properties as compared to images formed when a double layered member similar to the above members, except not containing surface skins at the interface, is split in the same manner.